Takayu Onsen Adachiya is a historic hot spring ryokan located at an elevation of approximately 750 meters on the slopes of the Azuma Mountain Range in Fukushima City, Fukushima Prefecture. Founded in 1607 (Keicho 12) by the first-generation owner Kanno Sanshiro, who is said to have discovered the hot spring following a divine message in a dream, the inn boasts over 400 years of history. Takayu Onsen is counted among the Three Great Takayu of Oshu alongside Zao Takayu and Shirabu Takayu, and has long been revered as a therapeutic bathing destination with the reputation of being a miraculous hot spring that heals within three days. The water is classified as an acidic sulfur-containing calcium-aluminum sulfate spring (hydrogen sulfide type) with a strongly acidic pH of 2.7, a source temperature of 45-46 degrees Celsius, and characteristically milky-white sulfurous water. All facilities in Takayu Onsen maintain 100% natural free-flowing source water with absolutely no dilution, heating, or circulation filtration. Adachiya is an adults-only inn (middle school age and above) offering refined hospitality including creative Japanese cuisine served around an irori hearth and complimentary drink services. The large outdoor bath Taiki no Yu was renovated in 2023 into separate male and female areas, with further renovations of the west outdoor bath and main bath scheduled for completion in summer 2025. Private outdoor baths Yakushi Ichi no Yu and Yakushi Ni no Yu are available at no additional charge. Day-trip bathing is also available at 1,500 yen for adults with a 90-minute time limit.